Lens array, image sensor, information processor and information processing system comprising the image sensor

ABSTRACT

An object of this invention is to provide a lens array in which the amount of light reaching the image forming surface is large and the variation in the amount of light is small. In order to achieve this object, the lens array comprises cylindrical graded index lenses of radius r 0  wherein the refractive index continuously decreases from the center of the lens toward the periphery, said cylindrical graded index lenses are arranged in one line or plural lines with array pitch 2R, if R is R≧r 0 ≧0.8R and if the refractive index profile of each graded index lens is approximated by n(r) 2 =n 0   2 {1−(g·r) 2 }, the overlapping degree m defined by m=X 0 /2R satisfies 1.05≦m≦1.2, wherein, said r is the distance from the optical axis, n(r) is refractive index at the distance r from the optical axis, n 0  is the refractive index at the center, g is the refractive index profile constant, X 0  is the radius of the field of view (X 0 =r 1  cos(Z 0 π/P), r 1  is the effective radius of the graded index lens, Z 0  is the length of the graded index lenses, and P is the period length of the graded index lenses namely P=2π/g.

TECHNICAL FIELD

This invention relates to a lens array, an image sensor, and aninformation processor comprising the image sensor and an informationprocessing system comprising the image sensor.

This application is based on Japanese Patent Application, No. Hei11-306060 filed in Japan, the content of which is incorporated herein byreference.

BACKGROUND ART

Heretofore, an image sensor unified with a lighting device to light adocument, a lens to form an image of the reflected light which isreflected by the document, and which has the information of thedocument, and a sensor to convert the reflected light image formed bythe lens into electrical signals is used as the reading device in afacsimile device, a scanner device, or other information processor.Lenses may be divided into two basic kinds: reduction type lens andequal size type lens. The reduction type lens forms an image which has asize reduced relative to the size of the object, and which is formed bythe reflected light from a document. The equal size type lens forms animage which has a size which is equal to an object, and which is formedb y the reflected light from a document.

Generally, the latter equal size type lens is often used as the shape ofa so called lens array that has many lens elements arranged in line of alength equivalent to the width of a document.

Recently, the reduction type lens which requires a long optical pathlength is not used very much because of the desire to miniaturizeinformation processors such as facsimile devices and scanner devices.Furthermore, the lens array which comprises the equal size type lens inwhich the optical path length is short is common.

The cylindrical lens which has a continuous refractive index profileinside is used as the equal size type lens. A lens, made of glass whichhas a continuous refractive index profile inside, was already proposedin Japanese Examined Patent Application, Second Publication No. Sho47-816. Furthermore, a lens made of plastic which has a continuousrefractive index profile inside was proposed in Japanese Examined PatentApplication, Second Publication No. Sho 47-28059. Subsequently, the lensmade of glass by various techniques and a lens made of plastic byvarious techniques were proposed. Generally both end surfaces of thesegraded index lenses are polished to mirror-finished surfaces which arevertical to the center axes of these lenses, and which are parallelmutually. Furthermore, these graded index lenses are used singly and asa micro-lens. Furthermore, the lens array in which a plurality of theselenses are arranged and adhered and unified is widely used as a part ofline sensors used in copying machines, facsimile machines, scanners, andso on. Furthermore, the lens array is widely used as the writing devicesused in LED printers and so on.

In addition, the range in which one lens forms an image of a size equalto that of an object is a circle of radius X₀ (radius of the field ofview). The amount of light is the greatest at the optical axis anddecreases with distance from the optical axis. The lens array causes avariation in the amount of light in t he length direction of the arraywith a period of the array pitch (2R) of the lens. The variation in theamount of light depends on the overlapping degree m defined by m=X₀/2R.

A lens array designed so that the overlapping degree m satisfies1.61≦m≦1.80 or 2.06≦m≦2.50 to make the variation in the amount of lightsmall is disclosed in Japanese Unexamined Patent Application, FirstPublication No. Hei 11-64605.

However, there is a problem in that the amount of light reaching a lightreceiving sensor is reduced in this lens array because the overlappingdegree m thereof is large and the radius X₀ of the field of view islarge when an image sensor is composed by using this lens array.Therefore, the lens for a color scanner of the type whose chromaticaberration is small may be used in this lens array. However, generallyan aperture angle is 15 degrees or less with this lens, that is, it issmall. Therefore, the amount of light which can be taken in is ½ or lesswith this lens in comparison with a lens with an aperture angle of about20 degrees typically used for a monochrome image sensor. Therefore, whenthis image sensor is used, it is necessary to lower the reading speed inaccordance with the ability of the light receiving sensor. Furthermore,according to this, it becomes easy to be influenced by noise factorssuch as outside light.

Furthermore, the difference of conjugate length TC between eachwavelength of RGB increases when the overlapping degree m is enlargedthat when there is some chromatic aberration in the lens. Then, colorblurring appears in the color image sensor comprising this lens.Furthermore, the resolution of the color image sensor comprising thislens is low.

DISCLOSURE OF INVENTION

An object of this invention is to provide a lens array in which theamount of light reaching the image forming surface is large and thevariation in the amount of light is small. Furthermore, an object ofthis invention is to provide an image sensor in which reading speed ishigh, and an information processor comprising it. Reading speed of theimage sensor is high even when a lens whose aperture angle is small andwhose chromatic aberration is small, that the amount of light which canbe taken in is small is used, by using the lens array in which theamount of light reaching the light receiving sensor is large.Furthermore, another object of this invention is to provide an imagesensor whose resolution is high even if a lens with some chromaticaberration is used, and an information processor comprising it.

A point of this invention is that the lens array comprises cylindricalgraded index lenses of radius r₀ wherein the refractive indexcontinuously decreases from the center of the lens toward the periphery,said cylindrical graded index lenses are arranged in one line or plurallines with array pitch 2R, if R is R≧r₀≧0.8R and if the refractive indexprofile of each graded index lens is approximated by n(r)²=n₀²{1−(g·r)²}, the overlapping degree m defined by m=X₀/2R satisfies1.05≦m≦1.2, wherein, said r is the distance from the optical axis, n(r)is the refractive index at the distance r from the optical axis, n₀ isthe refractive index at the center, g is the refractive index profileconstant, X₀ is the radius of the field of view (X₀=−r₁ cos(Z₀/P), r₁ isthe effective radius of the graded index lens, Z₀ is the length of thegraded index lenses, and P is the period length of the graded indexlenses namely P=2π/g.

Furthermore, a point of this invention is that in the lens array theaperture angle of said graded index lens is 15 degrees or less.

Furthermore, a point of this invention is that in the lens array R isR>r₀≧0.8R.

Furthermore, a point of this invention is that in the lens array theoverlapping degree m is 1.1≦m ≦1.2.

Furthermore, a point of this invention is that in the lens array saidgraded index lens is made of plastic.

Furthermore, a point of this invention is that in the lens array saidgraded index lens is made of glass.

Furthermore, a point of this invention is that the image sensorcomprises a lighting device which lights a document, said lens arraywhich makes reflected light from a document form an image, and anopto-electronic conversion device which receives the light of the imageformed by said graded index lens.

Furthermore, a point of this invention is that the image sensorcomprises the lens array wherein an interval Lm between the end surfaceof one side of said graded index lens and the document satisfies0.95·L₀≦Lm≦1.05·L₀ with the air layer conversion, and wherein aninterval Ls between the end surface of the other side of said gradedindex lens and the sensor satisfies 0.95·L₀≦Ls≦1.05·L₀ with the airlayer conversion, wherein said L₀ is L₀=−(1/n₀g)·tan(Z₀π/P).

Furthermore, a point of this invention is that in the image sensor theilluminant of said lighting device is an LED.

Furthermore, a point of this invention is that in the image sensor theilluminant of said lighting device comprises plural LEDs emittingwavelengths which are different from each other.

Furthermore, a point of this invention is that in the image sensor theilluminant of said lighting device comprises plural LEDs emittingwavelengths of three colors that are equivalent to blue, green, and red,and that are different from each other.

Furthermore, a point of this invention is that the information processorcomprises said image sensor and a processing means which processes theimage information inputted from said image sensor.

Furthermore, a point of this invention is that the information processorcomprises said image sensor, a means which changes the relative positionbetween a document and the image sensor, an image forming means whichforms an image from the image information read with said image sensor,and a control means which controls from input of a document to output.

Furthermore, a point of this invention is that the in formationprocessor comprises said image sensor, an analog signal processing meanswhich processes an analog signal from said image sensor, a convertingmeans which converts said analog signal into a digital signal, a digitalsignal processing means which processes said digital signal from saidconverting means, and an interface means which connects with the outsideapparatus.

Furthermore, a point of this invention is that the informationprocessing system comprises said information processor and a computerconnected with said information processor, wherein said interface meansbuilt in said information processor and the second interface means builtin said computer are connected to each other, and wherein a digitalsignal is transmitted and received through these interface means.

The variation in the amount of light of the lens array of the imagesensor of this invention is small, and the amount of light thereof ishigh, and the apparent chromatic aberration thereof is small. Therefore,there is a little blurring due to chromatic aberration, and reading withvivid high resolution in which the variation in the amount of light issmall can be realized.

Furthermore, an information processor and an information processingsystem of this invention can process high quality images read by theimage sensor.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross section of the image sensor of this invention.

FIG. 2 is a top view of the image sensor of this invention.

FIG. 3 is a side view of the lighting device used by this invention.

FIG. 4 is detailed figure of the lighting device used by this invention.

FIG. 5 is detailed figure of the lens array used by this invention.

FIG. 6 is a cross section of the information processor of thisinvention.

FIG. 7 is a functional block diagram of the information processor ofthis invention and the computer.

FIG. 8 is a figure which shows the outline of the resolution (MTF)measuring device of lenses.

BEST MODE FOR CARRYING OUT THE INVENTION

A lens array, an image sensor, and an information processor whichcomprises this image sensor of this invention and an informationprocessing system which comprises this image sensor of this inventionare explained in detail below.

The image sensor of this invention is composed by an opto-electronicconversion device which receives light, a lighting device, and a lensarray in which plural graded index lenses are arranged in line. Eachgraded index lens forms the image of the reflected light from a documenton said opto-electronic conversion device.

The lens array of this invention is the one in which cylindrical gradedindex lenses of the radius r₀ are arranged in line.

Both glass and plastic graded index lens are good. A lens made ofplastic is especially desirable because it is cheap and easy to process.

The radius r₀ of cylindrical graded index lens is desired to be 0.1 mmor more, and to be 1 mm or less. When r₀ is smaller than 0.1 mm, it islikely to be difficult to make a lens array. The lens array in which r₀is larger than 1 mm tends not to be practical because the length Z₀ ofthe lens array becomes too large.

The graded index lens used in this invention has a refractive indexprofile that continuously decreases from the center toward theperiphery. Desirably, the refractive index profile of said lens is theone in which the range of 0.2r₀˜0.7r₀ can be approximated by n(r)²=n₀²{1−(g·r)²} at least, wherein, r: the distance from the optical axis;n(r): the refractive index at the distance r from the optical axis; n₀:the refractive index at the center; and g: the refractive index profileconstant.

The effective radius r₁ of the lens used for this invention is r₁≦r₀. Aneffective radius means the radius of the transparent part for the lightof the wavelength used. The neighborhood of the periphery of the lensused for this invention may be opaque to avoid flaring light andcrosstalk light which do not to contribute to image forming.

Furthermore, the aperture angle of the lens used by this invention isdesired to be 15 degrees or less to improve the characteristics of thelens array, especially the focus depth characteristics.

The lens array used by this invention can be made by an optionalpublicly known method using graded index lenses. For example, it can bemade by a method in which several graded index lenses are arranged inparallel at a fixed pitch, and are fixed on a board with an adhesive,etc., and are cut to fixed length Z₀, and end surfaces of the lenses arepolished.

The array pitch of lenses means a distance between the center axes ofthe lenses located next to each other, and is shown with 2R. R and theradius r₀ of the lens in the lens array of this invention satisfyR≧r₀≧0.8R. Desirably, R and the radius r₀ of the lens satisfy R>r₀≧0.8R.The amount of light of the lens array can be enlarged by satisfyingr₀≧0.8R. Reading speed can be improved when this lens array is used forthe image sensor, even when the lens whose aperture angle is small andwhose chromatic aberration is small is used. Furthermore, R becomes R=r₀when lenses are arranged to touch each other perfectly. By satisfyingR>r₀, crosstalk between lenses is prevented, and the resolution of thelens array can be improved, and it becomes easy to obtain theoverlapping degree m in the range of this invention mentioned later, andthe total number of lenses used for the lens array can be reduced.Therefore, it is economical.

The overlapping degree m defined by m=X₀/2R of the lens array of thisinvention satisfies 1.05≦m≦1.2 (wherein, r: a distance from the opticalaxis; n(r): the refractive index at the distance r from the opticalaxis; n₀: the refractive index at the center; g: the refractive indexprofile constant; X₀: the radius of the field of view (X₀=−r₁cos(Z₀π/P)), r₁: the effective radius of the graded index lenses; Z₀:the length of the graded index lenses; and P: the period length of thegraded index lenses (P=2π/g)). Desirably, m satisfies 1.1≦m≦1.2.

The amount of light at the image forming surface of the lens array isenlarged and the variation in the amount of light can be reduced bymoving the overlapping degree m to the above-mentioned range.Furthermore, the image sensor in which reading speed is high can beobtained by using the lens array for the image sensor, even when thelenses in which aperture angle is small and chromatic aberration issmall are used, because the amount of light reaching the light receivingsensor is large. Furthermore, even if the lens with chromatic aberrationis used, the image sensor whose resolution is high can be obtained.

It is desirable that the interval Lm (air layer conversion) between theend surface of the graded index lens and a document satisfies0.95·L₀≦Lm≦1.05·L₀, and that the interval Ls (air layer conversion)between the end surface of the lens and the sensor satisfies0.95·L₀≦Ls≦1.05·L₀ in the image sensor of this invention (wherein,L₀=−(1/n₀g)·tan(Z₀π/P)).

The lens satisfying such a condition forms an image of the reflectionlight from a document on the sensor under the conditions close to theideal conditions of the variation in the amount of light and resolution.Therefore, the image sensor in which the variation in the amount oflight is smaller and in which the resolution is higher can be obtained.Resolution tends to decrease and the variation in the amount of lighttends to increase when Lm and Ls are out of the above range, becausedeviation from the erect equal size image increases.

The image sensor of this invention is composed of a sensor array 1, alens array 2, a lighting device 3, a cover glass 4 and a frame 5 asshown in the cross section of FIG. 1 and the top view of FIG. 2. In thesensor array 1, the sensor ICs 12 comprising line-shaped opto-electronicconversion devices are arranged in lines precisely on the sensor board11. The number of the sensor ICs 12 corresponds to the length of adocument read by the sensor array. The cover glass 4 consists ofoptically transparent components. The frame 5 establishes thosepositions and holds them.

Furthermore, 322 is a warp correction pin. In the manufacture of theimage sensor, the warp correction pin 322 of the lighting device 3 andthe top surface of the lens array 2 are first pressed against the coverglass 4. In this state, the cover glass 4 is bonded to the inner sidesurface of set frame 5 in the condition that the top surface of the lensarray 2, the frame 5 and the lighting device 3 are on the same planeapproximately, and that the lighting device 3 and the lens array 2 arcput between right and left inner surfaces of the frame 5. By thismethod, the lighting device 3 and the lens array 2 can be decided theseposition precisely and fixed without warp. Therefore, light can beirradiated properly at the desired lighting position. Therefore, thereflection light from a document can form the image in focus over theentire length of the lens array 2.

The lighting device 3 used with the image sensor of this invention isfor lighting a document. An incandescent lamp, a cold-cathode tube, LED,etc. are used as the illuminant of the lighting device 3. Thisilluminant may be combined with a filter element for the purpose ofcutting the light of the specific wavelength. An LED is desirably usedas the illuminant of the lighting device 3 because it is easy to use thelight of a specific wavelength. Furthermore, composing a color imagesensor of several kinds of LEDs with wavelengths which are differentfrom each other is more desirable. It is especially desirable that theilluminant is composed by plural LEDs with wavelengths of three colorsthat are equivalent to blue, green, and red, and that are different fromeach other. When the sensor is used as a color image sensor, it isdesirable to make the peak luminous wavelength 450˜480 nm (blue),510˜560 nm (green), 600˜660 nm (red), respectively, for the purpose ofimproving color reproduction. In the lighting device 3, the illuminantand the light guide are arranged so that light from the illuminantenters the light guide, and so that light going out of the light guidelights a document.

The side view of the lighting device is shown in FIG. 3, and the detailfigure of the lighting device is shown in FIG. 4. For example, thelighting device 3 is composed by the RGB 3-color LED illuminant 31 andthe light guide 32 which consists of part having excellent opticaltransparency such as an acrylic resin. The RGB 3-color LED illuminant 31is the part that LED elements of 3 colors including red (R) LED element311, green (G) LED element 312 and blue (B) LED element 313 asilluminants are packed in one package.

The RGB 3-color LED illuminant 31 is arranged so that the light from oneend or both ends along its length enters the light guide 32.Furthermore, the light entering the light guide 32 is transmitted in thelight guide 32 while repeating total reflection on the interface betweenthe light guide 32 and the air. And, the lead line 314 extends from theRGB 3-color LED illuminant 31.

Furthermore, as shown in the detail figure of the lighting device ofFIG. 4, in the light guide 32, the inner saw tooth part 321 havingminute saw teeth is formed continuously along the length of the lightguide 32. Then, only the light entering the inner saw tooth part 321among the light transmitted in the light guide 32 is different from thelight entering the other surfaces, and is reflected and changesdirection toward a document. Then, on the next interface between thelight guide 32 and the air, the light does not satisfy the condition ofthe total reflection angle, and goes out of the light guide 32 pointingto the desired direction.

Next, the detail configuration of the lens array 2 used in thisembodiment is shown in FIG. 5. The lens array 2 of this embodiment iscomposed by the lenses 21 having the refractive index profile. In thelens array 2, plural cylindrical lenses 21 are arranged in line, and areput between two sheets of the side boards 23. The cylindrical lens 21has functions as a lens by making the refractive index differentgradually from the center of the lens toward the periphery.

The sensor board 11 is the glass-epoxy board made of fiberglassimpregnated with epoxy resin, etc. or the ceramics board on whichelectric wiring is formed. The sensor IC 12 is the opto-electronicconversion device which converts light into electricity and which is ofthe CCD or CMOS type. The plural sensor ICs 12 are glued by adhesive onthe sensor board 11 in line precisely. Furthermore, the sensor IC 12 andthe sensor board 11 are connected to each other electrically through thegold wire 13.

The operation of the image sensor of this invention is explained below.The lighting device 3 lights a document which is pressed on the coverglass 4 and which is supported by the cover glass 4 from the obliquedirection, as changing the lights of three colors including R, Q and Bin turn. The lens array 2 forms the image of the reflected light havingthe color information of three colors including R, G, and B from adocument on the sensor IC 12. The sensor IC 12 converts the light havingthe color information of three colors including R, G, and B intoelectrical signals, and transmits the electrical signals to a system(not shown in the figure). The system processes the electrical signalscorresponding to three colors including R, G, and B, and reproduces acolor image.

Because the variation in the amount of light is small, the image sensorof this invention can read an image uniformly. Furthermore, becauseapparent chromatic aberration is small, the image sensor can be a colorimage sensor of high resolution. Furthermore, because the amount oflight is high, it is possible to make the speed of reading quickly.

Next, the information processor of this invention is explained. Theinformation processor of this invention comprises the image sensor ofthis invention and a processing means which processes the imageinformation inputted from said image sensor.

The example of the information processor (for example, a facsimilemachine) comprising the image sensor of this invention is shown in FIG.6. In FIG. 6, 700 is the image sensor, 701 is the feed roller to feed adocument to the reading position, 702 is the separation piece toseparate documents to a one-by-one sheet securely. 703 is the sendingroller which is set at the reading position of the image sensor 700 toregulate the position of the surface of a document read by the imagesensor 700, and to be used as the document sending means to send adocument. Said document sending means is desirable as a means to changerelative position between the image sensor 700 and the document becauseit is simple. It is possible that a means to move the image sensor isused instead of the document sending means. Furthermore, it is possibleto use both means together. W shown in figure is the recording medium ofthe form of a rolled paper. The image information read by the imagesensor 700, or transmitted from the outside in the case of the facsimiledevice and so on is formed here. 704 is the recording head used as theimage forming means and various heads such as a thermal head, a bubblejet recording head, etc. can be used for this recording head 704.Furthermore, both the serial type head and the line type head can beused for this recording head 704. 705 is the platen roller which sends arecording medium to the recording position by the recording head 704 andwhich regulates the position of the surface of the recording mediumrecorded by the recording head 704. 706 is the operation panel toreceive input of operation including indicating parts, etc., arrangedtherein. 707 is the system control board on which the control partcontrolling each section, the driving circuit for the opto-electronicconversion device, the processing part of the image information, thetransmitting part and the receiving part, and etc., arc put. 708 is thepower supply for the device.

This device is controlled by a microcomputer (control means) on thesystem control circuit board 707. Furthermore, the microcomputercontrols said image sensor 700. In other words, the microcomputercontrols the lighting of the lighting device 3 and the driving of thesensor array 1.

The processing to record the image signal read by the image sensor 700in the recording medium W, or the image processing to output the imagesignal outside is performed by the signal processing circuit (imageprocessing means) on the system control circuit board 707.

One example of the information processing system which provides theinformation processor comprising the image sensor 700 is shown in FIG.7. This information processing system is a system in which the imagereading device 150 including the image sensor 700 is connected to apersonal computer 160. The image information read by the image readingdevice 150 is sent to the personal computer 160. Or, the imageinformation is sent in a network furthermore.

In FIG. 7, 170 is the CPU as the first control means controlling thewhole of the image reading device 150. Furthermore, 700 is the imagesensor as the reading unit composed by said illuminant and CCD linesensor and so on to convert the image of a document to an image signal.Furthermore, 116 is the analog signal processing circuit to give analogprocessing such as gain control to the analog image signal outputtedfrom the image sensor 700.

Furthermore, 118 is the A/D converter to convert the output of theanalog signal processing circuit 116 to the digital signal. Furthermore,180 is the digital signal processing circuit to give the imageprocessing such as shading compensation processing, γ convertingprocessing and magnification converting processing to the output data ofthe A/D converter 118 by using the memory 122. Furthermore, 124 is theinterface (I/F) which outputs the digital image data given imageprocessing by the digital signal processing circuit 180 outside.

For example, the interface 124 follows the standard adopted for thepersonal computer such as SCSI or Bi-Centronics. The interface 124 isconnected to the personal computer 160.

The image processing means is composed by the analog signal processingcircuit 116, the A/D converter 118, the digital signal processingcircuit 180, and the memory 122.

The personal computer 160 as the second control means is equipped withthe magneto-optical disk drive, the hard disk drive, the floppy diskdrive, etc., as the outside memory apparatus or the assistant memoryapparatus 132.

134 is a display to indicate operations in the personal computer 160,and 133 is the mouse/keyboard to input commands, etc.

Furthermore, 135 is the interface to administer transmitting andreceiving of data, commands and the condition information of the imagereading device between the personal computer and the image readingdevice.

The reading directions toward the image reading device can be inputtedinto the personal computer 160 by the mouse/keyboard.

When the reading directions are inputted, the CPU 170 transmits thereading command to the image reading device through the interface 135.Furthermore, the personal computer controls the image reading device inaccordance with the control program stored in the ROM 137. Furthermore,this control program may be the one which is stored in the memory mediumbuilt in the assistant memory device 132, and which is read by RAM 138in the personal computer, and which is executed by CPU 136.

The information processor of this invention becomes more useful by beingused in such an information processing system.

The image sensor of this invention is explained by using the followingexample. Furthermore, the measurement of the lens performance (MTF) inthe example of this invention and the comparative example was performedby the following method.

MTF, which indicates the resolution of a lens, was measured by thefollowing method. First, the standard rectangle lattice 804 which hassome spatial frequency (line pair/mm, Lp/mm), the lens array 805, theilluminant 801, the filter 802, and the diffusion board 803 werearranged as shown in FIG. 8. Next, the lattice image was read by the CCDline sensor 806 put on the image forming surface, and the maximum value(i_(max)) and the minimum value (i_(MIN)) of the amount of light weremeasured, and MTF was calculated by the following formula.

MTF(%)=(i _(MAX) −i _(MIN))/(i_(MAX) +i _(MIN))×100

Spatial frequency is the number which indicates how many line pairs,namely sets of the combination of the white line and the black lineshown in the lattice 804 in FIG. 8 are put in a width of 1 mm.

First, the example of this invention is explained. The plastic lenses inwhich the radius r₀ is 0.297 mm, the effective radius r₁ is 0.250, therefractive index at the center is 1.497, the refractive index profileconstant g=0.486 (values are at 525 nm of the wavelength of light) werearranged in one line under the condition that the lenses were in contactwith one another and that the optical axis of the lenses were parallel.Then, these plastic lenses were put between two sheets of black colorbakelite boards, and were adhered with the epoxy resin adhesivedispersed carbon black. Then, one line of the lens array of the arraypitch 2R=0.597 mm, and the length of the lens Z₀=8.0 mm was made bycutting and polishing the end face of the lens by a diamond edge.Furthermore, adhesive was impregnated between the lenses at the time ofthe adhesion, and each lens was isolated by the adhesive because thelenses were pressed with a small pressure in the direction in whichlenses were adhered together at the time of the adhesion. The conjugatelength (TC) at which MTF at 470, 525, and 630nm of this lens arraybecame maximum was 14.7, 15.0, and 15.4 mm, respectively. Theoverlapping degree m at 525 nm of this lens array was 1.15, and L₀ was3.5 mm. MTF (12Lp/mm) and the variation in the amount of light at 470,525, and 630 nm at TC=15.0 mm of this lens array were measured. Themeasured value of MTF was 55, 77, and 55%, and the measured value of thevariation in the amount of light was 12, 8, and 18%, respectively.

The image sensor was made by putting the lens array in the color imagesensor under the condition that the interval Lm between the end surfaceand a document (air layer conversion) was 3.5 mm and that the intervalLs between the end surface and the sensor (air layer conversion) was 3.5mm. And a color image was transmitted by u sing this image sensor. As aresult, the transmission image including little blurring due to thechromatic aberration was obtained.

Next, the comparative example is explained. The comparative example wasthe same as said example of this invention except that the length of thelens Z₀ was 7.6 mm.

TC at which MTF at 470, 525, and 630 nm of this lens array becamemaximum was 17.2, 17.8, and 18.4 mm, respectively. The overlappingdegree m at 525 nm of this lens array was 1.55, and L₀ was 3.5 mm. MTF(12Lp/mm) and the variation in the amount of light at 470, 525, and 630nm at TC=15.0 mm of this lens array were measured. The measured value ofMTF was 40, 65, and 35%, and the measured value of the variation in theamount of light was 7, 9, and 8%, respectively. Furthermore, the amountof light of the lens array was about 80% of said example of thisinvention.

The image sensor was made by putting the lens array in the color imagesensor under the conditions in which the interval Lm between the endsurface and a document (air layer conversion) was 5.1 mm and that theinterval Ls between the end surface and the sensor (air layerconversion) was 5.1 mm. Furthermore a image was transmitted by usingthis image sensor. As a result, the transmission image includingblurring due to the chromatic aberration was obtained. The maximumreading speed of this image sensor was 20% below the image sensor ofsaid example of this invention.

Industrial Applicability

The variation in the amount of light of the lens array of the imagesensor of this invention is small, and the amount of light thereof islarge, and the apparent chromatic aberration thereof is small.Therefore, reading with little blurring due to chromatic aberration,vivid high resolution, and rare variation in the amount of light can berealized.

Furthermore, the information processor and the information processingsystem of this invention can process the high quality image read by theimage sensor.

What is claimed is:
 1. A lens array comprises cylindrical graded indexlenses of radius r₀ wherein the refractive index continuously decreasesfrom the center of the lenses toward the periphery, said cylindricalgraded index lenses are arranged in one line or plural lines with arraypitch 2R, if R is R≧r₀≧0.8R and if the refractive index profile of eachgraded index lens is approximated by n(r)²=n₀ ²{1−(g·r)²}, theoverlapping degree m defined by m=X₀/2R satisfies 1.05≦m≦1.2, whereinsaid r is the distance from the optical axis, n(r) is refractive indexat the distance r from the optical axis, n₀ is the refractive index atthe center, g is the refractive index profile constant, X₀ is the radiusof the field of view where X₀=−r1 cos(Z₀π/P), r₁ is the effective radiusof the graded index lens, Z₀ is the length of the graded index lenses,and P is the period length of the graded index lenses namely P=2π/g. 2.The lens array according to claim 1 wherein the aperture angle of saidgraded index lens is 15 degrees or less.
 3. The lens array according toclaim 1 wherein R is R>r₀≧0.8R.
 4. The lens array according to claim 1wherein the overlapping degree m is 1.1≦m≧1.2.
 5. The lens arrayaccording to claim 1 wherein said graded index lens is made of plastic.6. The lens array according to claim 1 wherein said graded index lens ismade of glass.
 7. An image sensor comprises a lighting device whichlights a document, the lens array which makes reflected light from adocument to form an image according to claim 1, and the opto-electronicconversion device which receives the light of the image formed by saidgraded index lens.
 8. The image sensor according to claim 7 whichcomprises the lens array wherein an interval Lm between the end surfaceof one side of said graded index lens and the document satisfies0.95·L₀≦Lm≦1.05·L₀ with the air layer conversion, and wherein aninterval Ls between the end surface of the other side of said gradedindex lens and the sensor satisfies 0.95·L₀≦Ls≦1.05·L₀ with the airlayer conversion, wherein said L₀ is L₀=−1/n₀g)·tan(Z₀π/P).
 9. The imagesensor according to claim 7 wherein the illuminant of said lightingdevice is an LED.
 10. The image sensor according to claim 8 wherein theilluminant of said lighting device is an LED.
 11. The image sensoraccording to claim 7 wherein the illuminant of said lighting devicecomprises plural LEDs emitting wavelengths which are different from eachother.
 12. The image sensor according to claim 8 wherein the illuminantof said lighting device comprises plural LEDs emitting wavelengths whichare different from each other.
 13. The image sensor according to claim 7wherein the illuminant of said lighting device comprises plural LEDsemitting wavelengths of three colors that are equivalent to blue, green,and red, and that are different from each other.
 14. The image sensoraccording to claim 8 wherein the illuminant of said lighting devicecomprises plural LEDs emitting wavelengths of three colors that areequivalent to blue, green, and red, and that are different from eachother.
 15. An information processor comprises the image sensor accordingto claim 7 and a processing means which processes the image informationinputted from said image sensor.
 16. An information processor comprisesthe image sensor according to any one of claims 8 to 14 and a processingmeans which processes the image information inputted from said imagesensor.
 17. An information processor comprises the image sensoraccording to claim 7, means which changes the relative position betweena document and the image sensor, an image forming means which forms animage from the image information read with said image sensor, and acontrol means which controls from input of a document to output.
 18. Aninformation processor comprises the image sensor according to any one ofclaims 8 to 14, means which changes the relative position between adocument and the image sensor, an image forming means which forms animage from the image information read with said image sensor, and acontrol means which controls from input of a document to output.
 19. Aninformation processor comprises the image sensor according to claim 7,an analog signal processing means which processes an analog signal fromsaid image sensor, a converting means which converts said analog signalinto a digital signal, a digital signal processing means which processessaid digital signal from said converting means, and an interface meanswhich connects with an outside apparatus.
 20. An information processorcomprises the image sensor according to any one of claims 8 to 14, ananalog signal processing means which processes an analog signal fromsaid image sensor, a converting means which converts said analog signalinto a digital signal, a digital signal processing means which processessaid digital signal from said converting means, and an interface meanswhich connects with an outside apparatus.
 21. An information processingsystem comprises the information processor according to claim 19 and acomputer connected with said information processor, wherein saidinterface means built in said information processor and a secondinterface means built in said computer are connected to each other, andwherein a digital signal is transmitted and received through saidinterface means and said second interface means.
 22. An informationprocessing system which comprises the information processor according toclaim 20 and a computer connected with said information processor,wherein said interface means built in said information processor and asecond interface means built in said computer are connected to eachother, and wherein a digital signal is transmitted and received throughsaid interface means and said second interface means.